Traditionally, physical fences have been used to contain livestock within defined areas. More recently, virtual fencing devices have been described for attachment to animals. Generally, these devices use the application of auditory and/or electrical stimuli to control the spatial location of the animal.
A number of inventions have addressed the issue of virtual fencing in general, but each of these devices rely on the presence of a central controller to determine, for example, the location of the animal, the location of virtual boundaries, when to apply and stop applying stimuli, etc. While these devices work satisfactorily, they are limited by inherencies of the detector devices used, eg the range of a GPS satellite network, locations of buried wires, location of a central transmitter and/or receiver, etc.
U.S. Pat. No. 5,241,923 (Janning) discloses a system for controlling animals using transponders and a central transmitter. This system may also be used to separate animals by affixing transponders to the animals in order to signal when they are getting too close, as determined by the central transmitter. This system applies stimulus to animals when the distance between them is less then the minimum distance programmed, without any communication between the transponders or determination, for example, as to which animal should receive the stimulus or for how long the stimulus should be applied.
One objective of the present invention is to provide a system for controlling and monitoring animals that can work when a central controller is out of reach or not present at all.